Dear Mr. Peter I also faced the same problem as Kurt faced, our diffractometer is the D8-advance model from Bruker... I took the scan using a PSD detector(Lynxeye) and got an increase of the error in peak position with increasing 2theta.. Again, when I extracted the dat file from the raw one.... i observed the rounded up values of 2theta(up to 2 decimal pt.) in the file. Now will the problem be optimized if I generate 2Theta values using a step which is rounded up upto a higher number of decimal point and replace them in place of my 2theta column? thanking you..
prasun ----- Original Message ----- From: "Peter Y. Zavalij" <pzava...@umd.edu> Date: Friday, January 9, 2009 7:17 pm Subject: RE: error in peak positions that is linear in theta > Kurt, > > It looks like incorrect step size (difference between actual step > size and > one that is written in the file) or incorrect distance to the > detector. The > later may incorrect step size if detector is PSD. > > I have similar situation with much smaller difference in peak > position but > the shift (difference between actual and written step size) varies > frommeasurement to measurement. Bruker is working on this but so > far no > solution/cause is known. > > Your case may be simpler if the difference is constant. Perhaps > calibrationof detector or its distance to the sample is needed. > > Best, > > > > Peter Zavalij > > > > X-ray Crystallographic Center > University of Maryland > > College Park, MD > > > > Office: (301)405-1861 > Lab: (301)405-3230 > > Fax: (301)314-9121 > > > > From: Kurt Leinenweber [ku...@asu.edu] > Sent: Thursday, January 08, 2009 6:09 PM > To: Rietveld_l@ill.fr > Subject: error in peak positions that is linear in theta > > > > Dear Rietvelders, > > > > (I hope this list is appropriate for this question). I am trying > to set up > a new D8 diffractometer from Bruker, and have it set up with a Vario > monochromator focusing on a sample in a capillary. Of course I > hope to do > Rietveld refinement on the samples eventually. But there is an > error in two > theta of the peak positions on all samples, and the error is > linear in two > theta. At 40 degrees the error (measured minus expected) is about > 0.020degrees, at 80 degrees the error is about 0.040 degrees, > etcetera. > > > Has anyone ever seen anything like this and do you know where it > could come > from? > > > > Thank you very much, > > > > - Kurt > > > > > > ********* > > Kurt Leinenweber > > Dept. of Chemistry and Biochemistry > > Arizona State University > > Tempe, AZ 85287-1604 > > > > phone (480)-965-8853 > > fax (480)-965-2747 > > > > *********** > > > >
